Examples of prior art three dimensional vertical NAND strings are illustrated in FIGS. 1A and 1B. The device shown in FIG. 1A is known in the art as terabit cell array transistor (“TCAT”) array. It includes damascened metal gate SONOS type cells in the vertical NAND flash string formed by a gate replacement process (see Jong, et al., “Vertical cell array using TCAT(Terabit Cell Array Transistor) technology for ultra high density NAND flash memory,” 2009 Symposium on VLSI Technology Digest of Technical Papers, pages 192-193, Jun. 16 2009, Honolulu, Hawaii, incorporated herein by reference in its entirety).
The device shown in FIG. 1B is known in the art as Pipe-shaped Bit Cost Scalable (“P-BiCS”) flash memory (see Katsumata, et al., “Pipe-shaped BiCS Flash Memory with 16 Stacked Layers and Multi-Level-Cell Operation for Ultra High Density Storage Devices,” 2009 Symposium on VLSI Technology Digest of Technical Papers, pages 136-137, Jun. 16 2009, Honolulu, Hawaii, incorporated herein by reference in its entirety).